The molding industry utilizes mold release agents for the removal of articles formed by a variety of molding mediums utilizing a variety of molds which are constructed utilizing a wide variety of materials. These mold release agents can be divided into several categories and are subdivided by their longevity (number of cycles between reapplication of the mold release agent.
Sacrificial release agents are one type of commonly used release agents. These release agents are general applied for each and every molding cycle. Sacrificial release agents exhibit little if any adhesion to the mold surface and release is provided by that failure with the release agent being removed from the mold surface and transferred or applied to the molded article. Sacrificial release agents further provide for excellent release ease of a molded article and accommodate to help keep mold surfaces clean preventing fouling and tarnish to the mold. However, the transfer of the sacrificial release agent to the molded article can deleteriously effect properties of the molded article such as adhesion between the article and a support apparatus (often referred to as an “insert”) which allows for support and/or mounting of the molded article, paintability, acceptance of an adhesive, or other attribute as the molded article is “coated” with a release agent. Because sacrificial release agents are not adherent to the mold surface, they require reapplication to the mold surface for each and every molding cycle and thus exhibit “no longevity” and increased labor, materials use, and cycle time.
Semi-permanent release agents are another type of release agent which is typically used. Semi-permanent release agents are applied at a particular amount and at a particular frequency of intervals such that multiple molded articles are produced and demolded from a single application of the semi-permanent release agent. Semi-permanent release agents exhibit adhesion to the mold surface. Release ease is generally provided by the formation of an interface on the mold surface which is not compatible with the medium being molded against it. A well formulated semi-permanent release agent provides for excellent release ease, excellent longevity (number of molding cycle between re-application), excellent molded part appearance (often referred to as “Cosmetics”), a minimal amount of transfer so as to not interfere with bonding to an insert, application of a paint or an adhesive, or other “post molding application”. However, transfer of the semi-permanent agent from the mold to the molded article can occur, causing similar deleterious effects as described for sacrificial release agents.
Finally, permanent release agents are another type of release agent typically used which is applied a single time and cured and remains on the mold surface until release efficacy is compromised whereupon they are removed and re-applied. Permanent release agents exhibit excellent adhesion to the mold surface. Release ease is provided by the adhesion of the permanent release agent to the mold, incompatibility with the medium being molded, and resistance to removal of the permanent release agent by the movement (action) of the mold medium against the agent (often referred to as “abrasion”).
Release ease, longevity and tool longevity can be accentuated by use of sacrificial, semi-permanent, and combination of the two over the top of the permanent release agent. For example, permanent release agents can be used in conjunction with either a sacrificial or a semi-permanent release agent to aid in release, ease, longevity (time between application of the sacrificial or semi-permanent) and lifetime (time between initial application of the permanent release agent and removal thereof). There are myriads of possible combinations of material utilized to comprise sacrificial, semi-permanent and permanent release agents. Common release agents can be comprised of oils, fatty acids and their salts, ‘waxes”, silicon based polymers, fluoropolymers and co-polymers, glycols, and (with no intention of any limitation) combinations of any and all of the above.
Production of semi-permanent release agents which exhibit excellent adhesion to the mold surface, excellent release of the molding medium from the mold, excellent cosmetics, resistance to transfer at least without deleterious effect on post molding processes to the molded article, excellent longevity, and excellent economics for the molder elude the molding industry.
Besides the conventional molding process involving metal or other rigid molds, some rubber objects, notably vehicle tires, are produced by placing an uncured so-called “green” tire over an inflatable elastomeric bladder, with the metal outside (tread and sidewall) mold surrounding the green tire. The bladder is heated and inflated, and then expands to enlarge the green tire, pressing it into the outside metal mold. The hot, green tire is kept under pressure and heat from the bladder until the rubber is cured, at which point the bladder is deflated, the tire removed, and the next green tire placed in the mold over the bladder.
The mold releases used for the metal molds may be any or a combination of the aforementioned sacrificial, semi-permanent, or permanent releases. However, the other surface which requires release is the interface between the bladder and the green tire. This is difficult because the release material must selectively adhere to one rubber surface and release from the other rubber surface.
Typically, the bladder/tire release material is painted or sprayed on to the inside of the green tires. The green tires must then sit and wait for the release material to dry and cure, which limits the rate of tire production. Release is usually not applied to the bladder because of the possibility of contaminating the metal mold surface.
One solution to this limiting step in tire manufacturing is to use a semi-permanent coating on the bladder. Prior art semi-permanent compositions are deficient because the release agents are often solvent based, thus creating volatile organic compounds (VOC) which have environmental and regulatory issues. Additionally, most of these prior art compositions evolve hydrogen gas during storage and use, presenting a fire and explosion hazard.
Thus, there remains an unmet need to have a water-based release agent that is VOC-free; that can be used in a semi-permanent fashion, thus reducing the number of applications, and that does not use hydrides, thus eliminating the production of hazardous hydrogen gas. In addition, there remains an unmet need for a release agent having the characteristics above that can be easily applied and rapidly cure to a green tire or bladder and provide multiple releases.